[PATCH 2/2] tracing: Sample module to demonstrate kernel access to Ftrace instances.
From: Divya Indi
Date: Wed Nov 20 2019 - 14:09:28 EST
This is a sample module to demonstrate the use of the newly introduced and
exported APIs to access Ftrace instances from within the kernel.
Newly introduced APIs used here -
1. Create/Lookup a trace array with the given name.
struct trace_array *trace_array_get_by_name(const char *name)
2. Destroy/Remove a trace array.
int trace_array_destroy(struct trace_array *tr)
4. Enable/Disable trace events:
int trace_array_set_clr_event(struct trace_array *tr, const char *system,
const char *event, bool enable);
Exported APIs -
1. trace_printk equivalent for instances.
int trace_array_printk(struct trace_array *tr,
unsigned long ip, const char *fmt, ...);
2. Helper function.
void trace_printk_init_buffers(void);
3. To decrement the reference counter.
void trace_array_put(struct trace_array *tr)
Sample output(contents of /sys/kernel/tracing/instances/sample-instance)
NOTE: Tracing disabled after ~5 sec)
_-----=> irqs-off
/ _----=> need-resched
| / _---=> hardirq/softirq
|| / _--=> preempt-depth
||| / delay
TASK-PID CPU# |||| TIMESTAMP FUNCTION
| | | |||| | |
sample-instance-1452 [002] .... 49.430948: simple_thread: trace_array_printk: count=0
sample-instance-1452 [002] .... 49.430951: sample_event: count value=0 at jiffies=4294716608
sample-instance-1452 [002] .... 50.454847: simple_thread: trace_array_printk: count=1
sample-instance-1452 [002] .... 50.454849: sample_event: count value=1 at jiffies=4294717632
sample-instance-1452 [002] .... 51.478748: simple_thread: trace_array_printk: count=2
sample-instance-1452 [002] .... 51.478750: sample_event: count value=2 at jiffies=4294718656
sample-instance-1452 [002] .... 52.502652: simple_thread: trace_array_printk: count=3
sample-instance-1452 [002] .... 52.502655: sample_event: count value=3 at jiffies=4294719680
sample-instance-1452 [002] .... 53.526533: simple_thread: trace_array_printk: count=4
sample-instance-1452 [002] .... 53.526535: sample_event: count value=4 at jiffies=4294720704
sample-instance-1452 [002] .... 54.550438: simple_thread: trace_array_printk: count=5
sample-instance-1452 [002] .... 55.574336: simple_thread: trace_array_printk: count=6
Signed-off-by: Divya Indi <divya.indi@xxxxxxxxxx>
Reviewed-by: Aruna Ramakrishna <aruna.ramakrishna@xxxxxxxxxx>
---
samples/Kconfig | 7 ++
samples/Makefile | 1 +
samples/ftrace_instance/Makefile | 6 ++
samples/ftrace_instance/sample-trace-array.c | 131 +++++++++++++++++++++++++++
samples/ftrace_instance/sample-trace-array.h | 84 +++++++++++++++++
5 files changed, 229 insertions(+)
create mode 100644 samples/ftrace_instance/Makefile
create mode 100644 samples/ftrace_instance/sample-trace-array.c
create mode 100644 samples/ftrace_instance/sample-trace-array.h
diff --git a/samples/Kconfig b/samples/Kconfig
index d63cc8a..1c7864b 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -20,6 +20,13 @@ config SAMPLE_TRACE_PRINTK
This builds a module that calls trace_printk() and can be used to
test various trace_printk() calls from a module.
+config SAMPLE_TRACE_ARRAY
+ tristate "Build sample module for kernel access to Ftrace instancess"
+ depends on EVENT_TRACING && m
+ help
+ This builds a module that demonstrates the use of various APIs to
+ access Ftrace instances from within the kernel.
+
config SAMPLE_KOBJECT
tristate "Build kobject examples"
help
diff --git a/samples/Makefile b/samples/Makefile
index debf892..02c444e 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -17,6 +17,7 @@ obj-$(CONFIG_SAMPLE_RPMSG_CLIENT) += rpmsg/
subdir-$(CONFIG_SAMPLE_SECCOMP) += seccomp
obj-$(CONFIG_SAMPLE_TRACE_EVENTS) += trace_events/
obj-$(CONFIG_SAMPLE_TRACE_PRINTK) += trace_printk/
+obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += ftrace_instance/
obj-$(CONFIG_VIDEO_PCI_SKELETON) += v4l/
obj-y += vfio-mdev/
subdir-$(CONFIG_SAMPLE_VFS) += vfs
diff --git a/samples/ftrace_instance/Makefile b/samples/ftrace_instance/Makefile
new file mode 100644
index 0000000..3603b13
--- /dev/null
+++ b/samples/ftrace_instance/Makefile
@@ -0,0 +1,6 @@
+# Builds a module that calls various routines to access Ftrace instances.
+# To use(as root): insmod sample-trace-array.ko
+
+CFLAGS_sample-trace-array.o := -I$(src)
+
+obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += sample-trace-array.o
diff --git a/samples/ftrace_instance/sample-trace-array.c b/samples/ftrace_instance/sample-trace-array.c
new file mode 100644
index 0000000..d523450
--- /dev/null
+++ b/samples/ftrace_instance/sample-trace-array.c
@@ -0,0 +1,131 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/module.h>
+#include <linux/kthread.h>
+#include <linux/trace.h>
+#include <linux/trace_events.h>
+#include <linux/timer.h>
+#include <linux/err.h>
+#include <linux/jiffies.h>
+
+/*
+ * Any file that uses trace points, must include the header.
+ * But only one file, must include the header by defining
+ * CREATE_TRACE_POINTS first. This will make the C code that
+ * creates the handles for the trace points.
+ */
+#define CREATE_TRACE_POINTS
+#include "sample-trace-array.h"
+
+struct trace_array *tr;
+static void mytimer_handler(struct timer_list *unused);
+static struct task_struct *simple_tsk;
+
+/*
+ * mytimer: Timer setup to disable tracing for event "sample_event". This
+ * timer is only for the purposes of the sample module to demonstrate access of
+ * Ftrace instances from within kernel.
+ */
+static DEFINE_TIMER(mytimer, mytimer_handler);
+
+static void mytimer_handler(struct timer_list *unused)
+{
+ /*
+ * Disable tracing for event "sample_event".
+ */
+ trace_array_set_clr_event(tr, "sample-subsystem", "sample_event",
+ false);
+}
+
+static void simple_thread_func(int count)
+{
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule_timeout(HZ);
+
+ /*
+ * Printing count value using trace_array_printk() - trace_printk()
+ * equivalent for the instance buffers.
+ */
+ trace_array_printk(tr, _THIS_IP_, "trace_array_printk: count=%d\n",
+ count);
+ /*
+ * Tracepoint for event "sample_event". This will print the
+ * current value of count and current jiffies.
+ */
+ trace_sample_event(count, jiffies);
+}
+
+static int simple_thread(void *arg)
+{
+ int count = 0;
+ unsigned long delay = msecs_to_jiffies(5000);
+
+ /*
+ * Enable tracing for "sample_event".
+ */
+ trace_array_set_clr_event(tr, "sample-subsystem", "sample_event", true);
+
+ /*
+ * Adding timer - mytimer. This timer will disable tracing after
+ * delay seconds.
+ *
+ */
+ add_timer(&mytimer);
+ mod_timer(&mytimer, jiffies+delay);
+
+ while (!kthread_should_stop())
+ simple_thread_func(count++);
+
+ del_timer(&mytimer);
+
+ /*
+ * trace_array_put() decrements the reference counter associated with
+ * the trace array - "tr". We are done using the trace array, hence
+ * decrement the reference counter so that it can be destroyed using
+ * trace_array_destroy().
+ */
+ trace_array_put(tr);
+
+ return 0;
+}
+
+static int __init sample_trace_array_init(void)
+{
+ /*
+ * Return a pointer to the trace array with name "sample-instance" if it
+ * exists, else create a new trace array.
+ *
+ * NOTE: This function increments the reference counter
+ * associated with the trace array - "tr".
+ */
+ tr = trace_array_get_by_name("sample-instance");
+
+ if (!tr)
+ return -1;
+ /*
+ * If context specific per-cpu buffers havent already been allocated.
+ */
+ trace_printk_init_buffers();
+
+ simple_tsk = kthread_run(simple_thread, NULL, "sample-instance");
+ if (IS_ERR(simple_tsk))
+ return -1;
+ return 0;
+}
+
+static void __exit sample_trace_array_exit(void)
+{
+ kthread_stop(simple_tsk);
+
+ /*
+ * We are unloading our module and no longer require the trace array.
+ * Remove/destroy "tr" using trace_array_destroy()
+ */
+ trace_array_destroy(tr);
+}
+
+module_init(sample_trace_array_init);
+module_exit(sample_trace_array_exit);
+
+MODULE_AUTHOR("Divya Indi");
+MODULE_DESCRIPTION("Sample module for kernel access to Ftrace instances");
+MODULE_LICENSE("GPL");
diff --git a/samples/ftrace_instance/sample-trace-array.h b/samples/ftrace_instance/sample-trace-array.h
new file mode 100644
index 0000000..6f89624
--- /dev/null
+++ b/samples/ftrace_instance/sample-trace-array.h
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * If TRACE_SYSTEM is defined, that will be the directory created
+ * in the ftrace directory under /sys/kernel/tracing/events/<system>
+ *
+ * The define_trace.h below will also look for a file name of
+ * TRACE_SYSTEM.h where TRACE_SYSTEM is what is defined here.
+ * In this case, it would look for sample-trace.h
+ *
+ * If the header name will be different than the system name
+ * (as in this case), then you can override the header name that
+ * define_trace.h will look up by defining TRACE_INCLUDE_FILE
+ *
+ * This file is called sample-trace-array.h but we want the system
+ * to be called "sample-subsystem". Therefore we must define the name of this
+ * file:
+ *
+ * #define TRACE_INCLUDE_FILE sample-trace-array
+ *
+ * As we do in the bottom of this file.
+ *
+ * Notice that TRACE_SYSTEM should be defined outside of #if
+ * protection, just like TRACE_INCLUDE_FILE.
+ */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM sample-subsystem
+
+/*
+ * TRACE_SYSTEM is expected to be a C valid variable (alpha-numeric
+ * and underscore), although it may start with numbers. If for some
+ * reason it is not, you need to add the following lines:
+ */
+#undef TRACE_SYSTEM_VAR
+#define TRACE_SYSTEM_VAR sample_subsystem
+
+/*
+ * But the above is only needed if TRACE_SYSTEM is not alpha-numeric
+ * and underscored. By default, TRACE_SYSTEM_VAR will be equal to
+ * TRACE_SYSTEM. As TRACE_SYSTEM_VAR must be alpha-numeric, if
+ * TRACE_SYSTEM is not, then TRACE_SYSTEM_VAR must be defined with
+ * only alpha-numeric and underscores.
+ *
+ * The TRACE_SYSTEM_VAR is only used internally and not visible to
+ * user space.
+ */
+
+/*
+ * Notice that this file is not protected like a normal header.
+ * We also must allow for rereading of this file. The
+ *
+ * || defined(TRACE_HEADER_MULTI_READ)
+ *
+ * serves this purpose.
+ */
+#if !defined(_SAMPLE_TRACE_ARRAY_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _SAMPLE_TRACE_ARRAY_H
+
+#include <linux/tracepoint.h>
+TRACE_EVENT(sample_event,
+
+ TP_PROTO(int count, unsigned long time),
+
+ TP_ARGS(count, time),
+
+ TP_STRUCT__entry(
+ __field(int, count)
+ __field(unsigned long, time)
+ ),
+
+ TP_fast_assign(
+ __entry->count = count;
+ __entry->time = time;
+ ),
+
+ TP_printk("count value=%d at jiffies=%lu", __entry->count,
+ __entry->time)
+ );
+#endif
+
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+#define TRACE_INCLUDE_FILE sample-trace-array
+#include <trace/define_trace.h>
--
1.8.3.1